Abstract

Background

Fibroblast Growth Factors (FGF) and their receptors are well known for having major
implications in cell signalling controlling embryonic development. Recently, a gene
coding for a protein closely related to FGFRs (Fibroblast Growth Factor Receptors)
called FGFR5 or FGFR-like 1 (FGFRL1), has been described in vertebrates. An orthologous
gene was also found in the cephalochordate amphioxus, but no orthologous genes were
found by the authors in other non-vertebrate species, even if a FGFRL1 gene was identified
in the sea urchin genome, as well as a closely related gene, named nou-darake, in the planarian Dugesia japonica. These intriguing data of a deuterostome-specific gene that might be implicated in
FGF signalling prompted us to search for putative FGFRL1 orthologues in the completely
sequenced genomes of metazoans.

Results

We found FGFRL1 genes in the cnidarian Nematostella vectensis as well as in many bilaterian species. Our analysis also shows that FGFRL1 orthologous
genes are linked in the genome with other members of the FGF signalling pathway from
cnidarians to bilaterians (distance < 10 Mb). To better understand the implication
of FGFRL1 genes in chordate embryonic development, we have analyzed expression patterns
of the amphioxus and the mouse genes by whole mount in situ hybridization. We show that some homologous expression territories can be defined,
and we propose that FGFRL1 and FGF8/17/18 were already co-expressed in the pharyngeal
endoderm in the ancestor of chordates.

Conclusion

Our work sheds light on the existence of a putative FGF signalling pathway actor present
in the ancestor of probably all metazoans, the function of which has received little
attention until now.